Polysilicon rod and method for manufacturing polysilicon rod

ABSTRACT

A polysilicon rod wherein in an area whose distance from a center of a cross section of the polysilicon rod is within ⅔ of a radius and that excludes a seed core, average grain boundary characteristics have following features:
         a coincidence grain boundary ratio exceeds 20%, a grain boundary length exceeds 550 mm/mm 2 , and a random grain boundary length does not exceed 800 mm/mm 2 .

TECHNICAL FIELD

The present invention relates to raw polysilicon for improving thedefect rate in the manufacture of single crystal and a method formanufacturing the same.

The present application claims the priority of Japanese PatentApplication No. 2020-108123 filed on Jun. 23, 2020, the contents ofwhich are entirely incorporated by reference.

BACKGROUND ART

In the manufacture of semiconductor devices, the manufacturing processof single crystal silicon is required to control impurities, latticedefects, etc., and maintain productivity. Examples of the currentlymainstream method for manufacturing single crystal include a floatingzone (FZ) method and a Czochralski (CZ) method. Of the two methods, theFZ method is a method of directly heating a polysilicon rod byhigh-frequency heating to obtain single crystal, which has more featuresfavorable for controlling impurities than the CZ method using a quartzcrucible.

A defect in the FZ method means that single crystal growth is inhibitedand dislocation occurs, and a crystal defect is caused in a singlecrystal rod. One of the factors that inhibit the single crystal growthis a phenomenon in which polysilicon is left unmelted to cause thedefect.

In this FZ method, the crystal characteristics of the raw polysiliconrod used are greatly associated with the defect in the FZ that occursduring the manufacture of single crystal.

In the course of the single crystal growth in the FZ method, theoccurrence of the defect in the FZ is an important problem because itsignificantly lowers productivity.

Manufacture of polysilicon rods as a raw material in the FZ method ismainly performed by a Siemens method that is a CVD method in whichsilane gas as a raw material is precipitated on a heated silicon rod inthe air.

Each of JP 2008-285403 A, JP 2013-193902 A, JP 2014-28747 A, and JP2017-197431 A discloses a polysilicon rod characterized by its acicularcrystal, area ratio of coarse grains, and size of a crystal grain. Eachof JP 2013-217653 A, JP 2015-3844 A, and JP 2016-150885 A discloses amethod for selecting a single crystal raw material according to the peakintensities and the numbers of peaks of Miller indices <111> and <220>by an X-ray diffraction method. JP 2019-19010 A discloses a polysiliconrod characterized by the size of a crystal grain and the diffractionintensity of a Miller index <222> by an X-ray diffraction method.

SUMMARY OF INVENTION Problem to be Solved by Invention

(1) None of the methods of the aforementioned patent documents canprovide high quantitativeness and reproducibility. This is becauseattention has been paid to coarse grains of polysilicon (size,distribution, crystal orientation, etc.) as a cause of the singlecrystallization defect in the FZ method, which is insufficient alone.

The present invention provides a polysilicon rod in which the singlecrystallization defect in the FZ method is reduced by the ratio of thebreadth of a grain boundary surface to coincidence grain boundary, whichis a feature of a grain boundary that is a boundary surface betweenparticles.

For example, a silicon rod having the largest crystal grain is a singlecrystal silicon rod, and when a model in which this single crystalsilicon rod is single-crystallized by the FZ method is considered, itcan be said that the defect rate due to the raw material is zero. Whenthis single crystal is divided, a grain boundary surface appears. Acoincidence grain boundary closest to a single crystal bond is Σ3, and agrain boundary surface having no coincidence lattice point or having noregularity is a random grain boundary. It can be said that a grainboundary containing a large amount of Σ3 that is a bonding surfaceclosest to single crystal is close to single crystal.

(2) A reactor for performing a CVD reaction by the Siemens method isgenerally a bell jar type. The inner wall of a reactor receivesradiation from a heated rod. When the inner wall is in a mirror surfacestate, the reflectance is high and an effect of returning the radiantenergy from the rod to the rod can be obtained, but when the inner wallis fogged, the reflectance is decreased, so that the absorption of theenergy into the wall surface is increased and the energy is not returnedto the rod. The cause of the fogging is that chlorosilanes as a rawmaterial cause hydrolysis with the moisture in the air when the reactoris opened between batches, so that the reflectance tends to be decreasedwith each batch. As a result, it is difficult to manufacture polysiliconrods under the same conditions at all times. Polysilicon having adesired grain boundary can be manufactured by feeding back the grainboundary characteristics of the previous batch to the reactionconditions of the next batch.

Means for Solving Problem

An inhibitor for single crystallization by the FZ method is included inthe characteristics of a grain boundary surface, and by measuring andanalyzing it, and feeding back to the manufacturing conditions,polysilicon rods suitable for single crystallization by the FZ methodcan be manufactured.

When the single crystallization process of the FZ method is looked at,an area near the center of a polysilicon rod is easily affected by agrain boundary because it reaches a single crystal growth surfaceimmediately after being melted, while an area near the outer peripheryof the polysilicon rod is less affected than the area near the centerbecause it passes through a heating zone by an induced current.

Specifically, for the area to be the center at the time of singlecrystallization by the FZ method, an area having a small random grainboundary length and a large grain boundary length is favorable, and asthe distance from the center becomes larger, even an area having asmaller grain boundary length becomes acceptable.

Therefore, the rod containing polysilicon is beneficial, in which in anarea whose distance from the center of the cross section of thepolysilicon rod is within ⅔ of the radius and that excludes the seedcore, the average coincidence grain boundary ratio exceeds 20%, theaverage grain boundary length exceeds 550 mm/mm², and the average randomgrain boundary length does not exceed 800 mm/mm². Further, thepolysilicon rod is favorable, in which the coincidence grain boundaryratio exceeds 25%, the grain boundary length exceeds 650 mm/mm², and therandom grain boundary length does not exceed 700 mm/mm².

When it is applied to the entire polysilicon rod, the rod containingpolysilicon is beneficial, in which in an area including the entirepolysilicon rod but the seed core, the average coincidence grainboundary ratio exceeds 20%, the average grain boundary length exceeds550 mm/mm², and the average random grain boundary length does not exceed800 mm/mm². Further, the polysilicon rod is favorable, in which thecoincidence grain boundary ratio exceeds 25%, the grain boundary lengthexceeds 650 mm/mm², and the random grain boundary length does not exceed700 mm/mm².

The closer the coincidence grain boundary ratio is to 100%, the better.However, the manufacturing conditions for realizing this is close tothose for epitaxial film growth, so that there is little cost advantagewith current technology. In addition, when the grain boundary length isintended to be increased, it is also necessary to increase thecoincidence grain boundary ratio in order to reduce the random grainboundary length to 700 mm/mm² or less, so that it is realistic from theabove reason that the grain boundary length is 3000 mm/mm² or less.

In the method for manufacturing a polysilicon rod by the Siemens method,the environment inside a reactor gradually changes as described above.Therefore, it is considered that polysilicon is analyzed at constantintervals and the results are fed back to the CVD conditions. Thecoincidence grain boundary ratio that is a feature of a grain boundary,the grain boundary length that is an index of the breadth of a grainboundary, and the random grain boundary length obtained from them arequantitative values and characterized by being able to be associatedwith manufacturing conditions. Also, in product design, the grainboundary characteristics from the inner periphery to the outer peripheryof a polysilicon rod can be controlled, so that polysilicon rodsaccording to the requirements of customers can be provided.

According to one aspect of the present invention,

1. the defect rate in single crystallization by the FZ method can bereduced, and the yield and productivity can be improved, and

2. polysilicon rods can be stably manufactured by feedback from thegrain boundary characteristics to the manufacturing conditions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the relationship between a grain boundarylength and a coincidence grain boundary ratio;

FIG. 2 is a graph showing the relationship between a grain boundarylength and a Σ3 coincidence grain boundary ratio;

FIG. 3A is a view showing images of Σ3 coincidence grain boundaries;

FIG. 3B is a view showing images of Σ9 coincidence grain boundaries,

FIG. 3C is a view showing images of random grain boundaries, and Σ3 to49 coincidence grain boundaries;

FIG. 4 is a schematic view for explaining the outline of a measurementmethod 1 in an embodiment of the present invention; and

FIG. 5 is a schematic view for explaining the outline of a measurementmethod 2 in the embodiment of the present invention.

DETAILED DESCRIPTION

A horizontal plane orthogonal to the growth direction of a polysiliconrod is cut out, and the crystal orientations of the crystal grainsexposed on a measurement surface are entirely measured at an electronbackscatter diffraction (EBSD) step of 1 μm, whereby the state of agrain boundary is calculated from differences between theorientations/angles of adjacent crystals of the obtained data matrix. AΣ3 coincidence grain boundary means a grain boundary surface where onecoincidence lattice point appears with respect to three atoms, which canbe said to be a grain boundary surface closest to single crystal amongcoincidence grain boundaries. It can be said that when a grain boundaryhas more coincidence lattice points, the thermal and physical propertiesof the grain boundary are closer to those of single crystal.

Coincidence Grain Boundary Ratio

The Σ3 to 49 detected using an EBSD analysis software (TSL Solutions KK)are defined as coincidence grain boundaries. About 80% of all thecoincidence grain boundaries of Σ3 to 49 are occupied by Σ3 and Σ9, inwhich Σ3 is slightly more than Σ9. As the Σ value becomes larger, theinterval between coincidence lattice points becomes larger, whichbecomes closer to a random grain boundary. Therefore, in the presentembodiment, a coincidence grain boundary ratio is calculated by usingthe sum of Σ3 to Σ9 coincidence grain boundaries, which is adopted as anindex. Here, Σ1 means single crystal.

Since the grain boundary is a boundary between grains, it is obtained asa surface when surface observation is performed, so that the grainboundary is indicated as an area. However, the information obtained by ameasurement using an actual apparatus becomes a line (becomes the lengthof a boundary line around when surface observation is performed).

Therefore, in the present embodiment, the coincidence grain boundaryratio is defined as follows (see FIGS. 3A to 3C):

coincidence grain boundary ratio (%)=boundary lines of observedcoincidence grain boundaries/boundary lines of observed grainboundaries.

The boundary lines include boundary lines exceeding Σ49. The “boundarylines of observed grain boundaries” in the above expression are all thegrain boundaries observed by the above EBSD analysis software. In thepresent embodiment, the “Σ3 to 49” are referred to as coincidence grainboundaries as described above. The boundary lines in the coincidencegrain boundaries are about 50 to 60% of the “boundary lines of observedgrain boundaries.”

In the EBSD analysis software, the orientations (angles) of crystals onan observation surface are measured at intervals of, for example, 1 μmin the case of ×150. When there is a difference of a certain angle ormore in the changes in the obtained continuous data, it is regarded as agrain boundary. The coincidence grain boundaries of “Σ3 to 49” can beobtained from the orientations and directions of the crystals with thegrain boundary interposed therebetween.

It becomes boundary lines of observed grain boundaries>boundary lines of“Σ3 to 49 coincidence grain boundaries”>boundary lines of “Σ3 to Σ9coincidence grain boundaries”. The boundary lines of observed grainboundaries include the coincidence grain boundaries and grain boundariesthat are not the coincidence grain boundaries. Therefore, thecoincidence grain boundary ratio is obtained by dividing the sum of theboundary lines of “Σ3 to Σ9 coincidence grain boundaries” by the sum ofthe boundary lines of “Σ3 to 49 grain boundaries” and the boundary linesexceeding Σ49.

A grain boundary having a low coincidence lattice point density (a grainboundary close to a random grain boundary) has high energy and isunstable. Therefore, when there are many grain boundaries each having alow coincidence lattice point density, it triggers falling off ofunmelted particles on an FZ melt surface, causing an FZ defect. On theother hand, when a polysilicon rod having physical properties close tothose of single crystal is used as a raw material in the FZ method,stable melting can be obtained.

Grain Boundary Length

It is difficult to accurately measure the grain size of single crystalin polysilicon because a grain boundary surface cannot currently bedetermined by images of SEM or the like. By measuring the crystalorientation for each particle using the above EBSD or the like, thelength of a grain boundary on the measurement surface can be obtained,so that the average size of particles can be indirectly expressed. Whenthe sum of the length of grain boundaries on the measurement surface isdivided by the measured area, a grain boundary length per unit area canbe obtained. In the present embodiment, this is defined as a grainboundary length (unit: length/area) that is an index of the breadth of agrain boundary surface.

Random Grain Boundary Length

Various coincidence grain boundaries are included in the grainboundaries other than the Σ3 to Σ9 coincidence grain boundaries. As theΣ value becomes larger, the interval between the coincidence latticepoints becomes larger, so that the features of a grain boundary having alow Σ value (having low grain boundary energy and being stable) arelost. Therefore, the sum of Σs larger than Σ9 is defined as a randomgrain boundary, for convenience, and a random grain boundary length isdetermined from the grain boundary length per unit area. That is, whenthe sum of the length of grain boundaries which have Σs larger than Σ9on the measurement surface is divided by the measured area, a randomgrain boundary length per unit area can be obtained.

In order to reduce crystal defects and increase the yield in the FZmethod, it is favorable to use, as a raw material, one having a grainboundary length as long as possible, a low Σ value, a large coincidencegrain boundary ratio, and a small random grain boundary length. However,the coincidence grain boundary ratio and the grain boundary length arein a contradictory relationship for the most part. For example, in thepolysilicon manufactured under the condition of increasing thecoincidence grain boundary ratio, its grain boundary length is small.Therefore, it is important to find the best point for both the grainboundary characteristics.

The cause of the falling off of crystal particles, which inhibits singlecrystal growth, is that the bonding at a grain boundary surface is weakand unstable. As the number of random grain boundaries with less bondingof coincidence lattice points becomes larger, peeling off and fallingoff from the melt surface are more likely to occur. It can be said thatwhen of the grain boundary characteristics, the Σ value is small and thecoincidence grain boundary ratio is large, the bonding at a grainboundary surface is strong and stable, so that the falling off ofcrystal particles is less likely to occur. The falling off of crystalparticles due to a random grain boundary occurs at a temperature lowerthan the melting temperature of the single crystal because the energy atthe grain boundary surface is high. Therefore, the single crystalparticles that have fallen off are not sufficiently heated and melted,and reach the single crystal growth surface while the unmelted andsemi-melted particles are in a cluster form, causing a crystal defect.The unmelted and semi-melted particles depend on the sizes of thecrystal particles that have fallen off. The larger the size is, thelonger the existence time is, so that they are more likely to reach thesingle crystal growth surface.

Factors of the manufacturing conditions to obtain desired grain boundarycharacteristics include the temperature of the surface of a rod,reaction pressure, the concentration of silane as a raw material, etc.When a regression analysis is performed on these, a correlation ofR²=0.8 or more (R: coefficient of determination) is obtained. The sameapplies to a case where the number of parameters is further increasedand machine learning is used. The obtained correlation is used asfeedback to an apparatus, so that optimum reaction conditions thatfollows the changes in the state inside the reactor can be set.

While the diameters of the apparatuses are becoming larger In the FZmethod, conventional small-diameter apparatuses are also often used. Thegrain boundary characteristics required for each apparatus aredifferent. In even an apparatus of the same type, there are so-calledequipment peculiarities, but polysilicon rods that meet needs can bemanufactured by performing the present analysis.

As the measurement method, for example, an aspect (hereinafter, alsoreferred to as a “measurement method 1”) as shown in FIG. 4 may be used.The prepared silicon rod is cut at arbitrary positions (three positionsin the aspect shown in FIG. 4) and sliced, whereby samples are cut out.The samples thus obtained are measured. Since the characteristics ofboth the feet of a U-rod are basically the same, the measurement may beperformed only on one foot.

The measurement results show that in all the cut-out samples, the yieldin the FZ becomes good according to the following conditions in which:in an area whose distance from the center of the cross section of thepolysilicon rod is within ⅔ of the radius and that excludes the seedcore, the average coincidence grain boundary ratio exceeds 20%, theaverage grain boundary length exceeds 550 mm/mm², and the average randomgrain boundary length does not exceed 800 mm/mm²; or in an areaincluding the entire polysilicon rod but the seed core, the averagecoincidence grain boundary ratio exceeds 20%, the average grain boundarylength exceeds 550 mm/mm², and the average random grain boundary lengthdoes not exceed 800 mm/mm².

Therefore, it can be expected that favorable results will be obtainedeven with the polysilicon rods of subsequent batches that will bemanufactured under the same conditions. Since the wall surface of thereactor loses its luster and the efficiency of the radiant heat changesevery time a batch is processed, the environment inside the reactorgradually changes even under the same conditions, but this change is notdramatic. Therefore, for a certain period of time (e.g., for about onemonth), it can be expected that favorable results will be obtained evenwith polysilicon rods of batches that will be manufactured under thesame conditions.

When measurement results are favorable by meeting the above conditions,products with a good yield can be manufactured when the FZ is performedby using the foot that has not been cut out into slices in FIG. 4. Thefoot, from which the sliced samples are obtained in FIG. 4, may be usedas a chunk for the CZ.

For example, the procedure as described below can be taken.

Measurement is performed using the measurement method 1, and the foot,which is opposite to the foot that has passed by meeting the aboveconditions, is subjected to single crystal growth by the FZ (if themanufacturing apparatus is of the same type, one is regarded as arepresentative.).

At this time:

the measurement method 1 may be performed on every silicon rod in thesame chamber that has grown into a silicon core wire, and if they passby meeting the above conditions, the foot, which is opposite to the footthat has passed, may be subjected to single crystal growth by the FZ;

the measurement method 1 may be performed on a representative of thoseoutside the chamber, like the representative of those inside thechamber, and if it passes by meeting the above conditions, the rest ofthose may be subjected to single crystal growth by the FZ; or

one representative may be measured by the measurement method 1, and ifit passes by meeting the above conditions, the rest may be subjected tosingle crystal growth by the FZ.

In addition, areas near the electrode and the bridge are excluded fromthe viewpoint of quality, and the central portion having no cracks isused as an ingot for the FZ, so that, for example, an aspect as shown inFIG. 5 may be adopted as another measurement method.

According to the aspect (hereinafter, also referred to as a “measurementmethod 2”) in which an upper portion near the bridge and a lower portionnear the electrode are only cut out to make samples, as shown in FIG. 5,a rod for the FZ can also be acquired in the foot from which the sampleshave been made. A sample for quality evaluation is taken from a portionoutside the effective length of the ingot for the FZ, mainly from thevicinity of the electrode. The sample is analyzed to determine aresistance value, metal components, etc.

In the measurement method 2, for example, the following procedure can betaken.

A foot is measured by the measurement method 2, and the foot, which haspassed by meeting the above conditions, and its opposite foot are bothsubjected to single crystal growth by the FZ (if the manufacturingapparatus is of the same type, one is regarded as a representative.).

At this time:

all samples may be inspected by the measurement method 2, and rods,which have passed by meeting the above conditions, may be subjected tosingle crystal growth by the FZ;

the measurement method 2 may be performed on a representative of thoseoutside the chamber, like the representative of those inside thechamber, and if it passes by meeting the above conditions, all of thethose may be subjected to single crystal growth by the FZ method; or

one presentative may be measured by the measurement method 2, and if itpasses by meeting the above conditions, all may be subjected to singlecrystal growth by FZ.

If inspection results are different even when a manufacturing apparatusof the same type is used, or if the same silicon rods cannot bemanufactured even when manufactured under the same manufacturingconditions, either of the measurement methods 1 and 2 may be performedin each apparatus.

The cause of the case where characteristics are gradually lost as thelot is increased with the same apparatus is thought to be that depositsare deposited inside the bell jar, which leads to a decrease in theradiant heat.

Even in this case, the manufacturing conditions may be continuouslyreviewed, or the inside of the bell jar may be cleaned to return to theinitial state. However, if electropolishing is performed to clean theinside of the bell jar, the cost is highly expensive. Therefore, it is arealistic choice to continue to review the manufacturing conditions.

EXAMPLES

<Relationship Between FZ Results and Grain Boundary Characteristics>

Preparation of Polysilicon Rod

A crystal sample was prepared by the Siemens method usingtrichlorosilane and hydrogen as raw materials, the grain boundarycharacteristics were measured by EBSD, and the results of actualpull-out experiments by the FZ method are shown below. A sample, inwhich dislocation occurred in its crystal as a result of a singlecrystallization experiment by the FZ method, was determined as x(failure). The measurement results are also shown in FIG. 1.

TABLE 1 Coincidence Grain grain boundary Random grain boundary lengthboundary length FZ ratio % mm/mm² mm/mm² Determination 1 65  530 470 x 254 1030 190 ∘ 3 39 1400 850 x 4 50 1100 550 ∘ 5 41 1050 620 ∘ 6 45 1500830 x 7 50  830 420 ∘

Sampling for Grain Boundary Characteristics Measurement

Since it was not realistic to measure the grain boundary characteristicsof the entire rod, average grain boundary characteristics weredetermined by sampling.

1) Wafers each having a thickness of 10 mm were cut out from both endsof an effective length (the electrode side and the bridge side wereremoved) of a U rod taken out from a Siemens method CVD apparatus (seeFIG. 5).

2) A line segment a was drawn from the outer periphery to the seed coreof the wafer, the line segment a bisecting, on the acute angle side, theangle formed between lines that are drawn to extend from the outerperiphery to the seed core of the wafer in a portion where the line isthe largest and a portion where the line is shortest.

3) Samples were cut out at intervals of 20 mm from the core wire alongthe line segment a. For each sample, a measurement range of 0.5 mm×0.5mm or more was measured with an EBSD apparatus (manufactured by TIMInc.) Step of 1.0 microns, and average grain boundary characteristicswere determined. Note that calculation was performed in consideration ofperforming cylindrical grinding in a later step.

4) For sections in which reaction conditions (factors that affect agrain boundary, such as the temperature of a rod, reaction pressure, rawmaterial concentration, raw material supply speed, CVD apparatus, andradiant heat that a rod receives from outside) were the same in theradial growing direction throughout a reaction batch, thecharacteristics of the entire sections were determined by measuring arepresentative point.

<Example of Analysis of Reaction Conditions and Feedback>

An example is taken, in which: in an apparatus for manufacturingpolysilicon by the Siemens method, the apparatus having a function ofkeeping a constant temperature by generating heat by making a currentflow through the seed core of the polysilicon that is connected to theelectrode, and the gas phase portion of the apparatus being filled withhydrogen and chlorosilane, a deposited layer of polysilicon is formed onthe surface of the seed core of heated silicon, thereby forming apolysilicon rod.

As the reaction conditions, a chlorosilane concentration and thetemperature of the surface of the polysilicon rod during the CVDreaction were taken, and the relationships with grain boundarycharacteristics were analyzed. Results of the analysis are schematicallyshown in FIG. 2. Assuming that the point A is the current condition, thegrain boundary characteristics change in the direction of the point Bwhen the chlorosilane concentration is only changed to be higher fromthe condition of the point A. When the temperature of the rod is onlylowered from the condition of the point A, the grain boundarycharacteristics change in the direction of the point C. When thechlorosilane concentration is set to the condition of the point B andthe temperature of the rod is set to the condition of the point C,polysilicon having the grain boundary characteristics of the point D isobtained.

By applying the actual measurement results to FIG. 2 and maintaining thelatest state, optimal reaction conditions for obtaining a polysiliconrod with desired grain boundary characteristics can always be adjusted.

Method 1 of Feedback to Manufacturing Conditions:

As a method for designing the grain boundary characteristics from thecenter to the outer periphery of a polysilicon rod, the temperature ofthe surface of the rod is relatively raised in order to increase aregion where the coincidence grain boundary ratio is increased when thediameter is small, while the temperature of the surface of the siliconrod is made lower and the chlorosilane concentration is made higher (toprevent the heat inside the silicon rod from rising) in order toincrease the grain boundary length as the diameter becomes larger.Thereby, a polysilicon rod having a “proper region” can be manufactured.

Method 2 of Feedback to Manufacturing Conditions:

As the diameter becomes larger, a higher frequency is applied to raisethe temperature of the surface (by preventing the heat inside thesilicon rod from rising, the temperature of the surface can be raised),and the chlorosilane concentration in the chamber is made higher.Thereby, a polysilicon rod having a “proper region” can be manufactured.

What is claimed is:
 1. A polysilicon rod wherein in an area whosedistance from a center of a cross section of the polysilicon rod iswithin ⅔ of a radius and that excludes a seed core, average grainboundary characteristics have following features: a coincidence grainboundary ratio exceeds 20%, a grain boundary length exceeds 550 mm/mm²,and a random grain boundary length does not exceed 800 mm/mm².
 2. Thepolysilicon rod according to claim 1, wherein the coincidence grainboundary ratio exceeds 25%, the grain boundary length exceeds 650mm/mm², and the random grain boundary length does not exceed 700 mm/mm².3. The polysilicon rod according to claim 1, wherein the coincidencegrain boundary ratio does not exceed 90%, and the grain boundary lengthdoes not exceed 3000 mm/mm².
 4. A polysilicon rod wherein in an areaincluding the entire polysilicon rod but a seed core, average grainboundary characteristics have following features: a coincidence grainboundary ratio exceeds 20%, a grain boundary length exceeds 550 mm/mm²,and a random grain boundary length does not exceed 800 mm/mm².
 5. Thepolysilicon rod according to claim 4, wherein the coincidence grainboundary ratio exceeds 25%, the grain boundary length exceeds 650mm/mm², and the random grain boundary length does not exceed 700 mm/mm².6. The polysilicon rod according to claim 4, wherein the coincidencegrain boundary ratio does not exceed 90%, and the grain boundary lengthdoes not exceed 3000 mm/mm².
 7. A method for manufacturing a polysiliconrod according to claim 1, wherein manufacturing conditions are fed backby using a ratio of coincidence grain boundaries to all grain boundariesas an index that expresses a feature of a grain boundary; and by using avalue obtained by dividing a length of a grain boundary that hasappeared on a surface when the polysilicon rod is cut at an arbitraryposition by a measured area, as an index of a breadth of a grainboundary surface in polysilicon.
 8. The method for manufacturing apolysilicon rod according to claim 7, wherein a ratio of Σ3 to 9coincidence grain boundaries is used as an index that expresses afeature of a grain boundary.